In the discussion that follows, reference is made to certain structures and/or methods. However, the following references should not be construed as an admission that these structures and/or methods constitute prior art. Applicant expressly reserves the right to demonstrate that such structures and/or methods do not qualify as prior art against the present invention.
Doctor blades are used in many coating operations, including to level or remove excess material from a surface being coated and in releasing operations applied to products casted in thin layers (for example, tobacco). Typically, the angle of contact is controlled to achieve the desired result. Oscillation of the doctor blade, usually by oscillation of the entire doctor blade assembly, contributes to more even wear and more even coating as well as to an effective product release.
Typically, doctor blades are made of an inexpensive material and are replaced as they wear. Replacement can be by removal of the blade, usually removal of a blade and its holder (as in a so-called “cut-to-length” system), or by continuous or intermittent feeding of an elongated doctor blade to a blade holder (as in a so-called “pull through” system”). When fed continuously, the elongated doctor blade is typically unwound from a supply reel, fed into a blade holder, and wound on a take-up reel. Clamping systems operate to hold the doctor blade in operative position and also to advance the elongated doctor blade from supply reel to take-up reel. When the trailing end of one elongated doctor blade leaves the supply reel, the now empty reel is removed and replaced by a new supply reel containing a fresh coil of elongated doctor blade and, after any initial set up, the operation of the apparatus continued. Representative doctor blades and “pull through” system” doctor blade apparatus are disclosed in U.S. Pat. Nos. 5,007,132; 5,138,740, 5,264,035; and 5,782,976, the entire contents of which are incorporated herein by reference.